This invention relates to secondary petroleum recovery processes and more particularly to the prevention of plugging of porous structure formations by foreign substances in the waterflood liquids used in secondary recovery operations.
In secondary oil recovery operations the porosity of subterranean mineral formations is increased by injecting into the formation viscous liquids which fracture the formation. Aqueous liquids which contain swellable or gelable gums are often used as fracturing fluids. Typical of such gums are the polysaccharides such as guar gum, locust bean gum, gum tragacanth, gum agar, the alginates, etc. In practice, viscous gum-containing liquids are pumped into a formation under a sufficient pressure to create the desired extent of fracturing. Following the fracturing step the gum is hydrolyzed by injecting a hydrolyzing agent, such as an enzyme or an acid, into the formation. The formation is then backflushed to remove the hydrolyzed gum. After the fracturing fluid is removed from the formation, a fluid, such as clean water, is injected into the formation to increase the pressure in the formation. The increased pressure caused by this waterflooding facilitates the further removal of oil from the field. U.S. Pat. Nos. 3,058,909 and 3,079,332 describe the use of gums to fracture subterranean formations.
Due to environmental concerns or for economic reasons, it is usually desirable to reuse the water removed from the formation for subsequent formation fracturing or for waterflood operations. However, hydrolyzed gum-containing water cannot be efficiently used because the gum tends to plug up the channels of the formation. It would be desireable to find an economical and efficient method for removing hydrolyzed gums from aqueous fracturing fluids to permit the reuse of the aqueous fluid for subterranean oil recovery operations.